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From: jesse@camelot.sgi.com (Jesse Rendleman)
Newsgroups: comp.sys.sgi
Subject: Re: Silly error with flock
Message-ID: <1991Jan11.003748.3049@odin.corp.sgi.com>
Date: 11 Jan 91 00:37:48 GMT
References: <1991Jan9.030948.18665@ccu1.aukuni.ac.nz> <1991Jan10.214011.86@ux1.cso.uiuc.edu>
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In article <1991Jan9.030948.18665@ccu1.aukuni.ac.nz>, russell@ccu1.aukuni.ac.nz (Russell J Fulton;ccc032u) writes:
> I am trying to use flock but I always get an "Bad file number" error.
> Here is my test program:
> 
> #include <sys/types.h>
> #include <sys/file.h>
> #include <stdio.h>
> 
> main() {
>     int lock;
> 
>     lock = open("test.lock",O_RDONLY); /* test.lock does exist */
>     if ( lock <= 0) perror("open");
> 
>     if(flock(lock,LOCK_EX) == -1) perror("flock");
> 
>     getchar();
>     flock(lock,LOCK_UN);
>     close (lock);
> }
> 
> Always prints "flock: Bad file number"!
> 
> Any ideas?? It must be something so obvious that I have totally missed it!

from the flock(3b) man page...

     Unlike BSD flock(2), attempts to acquire an exclusive lock on an fd
     opened for reading but not writing will fail with EBADF, as will attempts
     to acquire a shared lock on a write-only fd.